The present disclosure relates to a multicolored display. More specifically, the exemplary embodiments of the present disclosure relate to a multicolored display having photochromic characteristics. In particular, the present exemplary embodiments are directed to marking particles comprising a mixture, i.e., a plurality of photochromic materials. Additionally, the present exemplary embodiments relate to a process for forming a multicolored display employing such marking particles. The exemplary embodiments are suitable for use in the display technology and are particularly suited for embedded display or marking technology.
Generally, photochromism is a reversible change of a single chemical species between two states having distinguishably different absorption spectra, wherein the change is induced in at least one direction by the action of electromagnetic radiation. The inducing radiation, as well as the changes in the absorption spectra, is usually in the ultraviolet, visible, or infrared regions. In some instances, the change in one direction is thermally induced. The single chemical species can be a molecule or an ion, and the reversible change in states may be a conversion between two molecules or ions, or the dissociation of a single molecule or ion into two or more species, with the reverse change being a recombination of the two or more species thus formed into the original molecule or ion.
Photochromic phenomena are observed in both organic compounds, such as anils, disulfoxides, hydrazones, oxazones, semicarbazones, stilbene derivatives, o-nitrobenzyl derivatives, spiro compounds, and the like, and in organic compounds, such as metal oxides, alkaline earth metal sulfides, titanates, mercury compounds, copper compounds, minerals, transition metal compounds such as carbonyls, and the like.
Photochromic materials are known in applications such as photochromic glasses, which are useful as, for example, ophthalmic lenses. It is also known to use a photochromic material in the printing or marking technologies. The use of a photochromic material in printing allows for the creation of unnoticeable, embedded or hidden images such as logos, text, watermarks, codes, etc. Hidden or embedded images may be desirable for authentication of the document, encryption, or the like. The use of a photochromic material to create an image allows the image to be hidden until exposed to a wavelength of light at which the photochromic material will absorb and undergo the photochromic process.
U.S. Pat. No. 5,633,109 (Jennings, et al.), the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises an aqueous liquid vehicle, a photochromic material, and a vesicle-forming lipid, wherein vesicles of the lipid are present in the ink.
U.S. Pat. No. 5,593,486 (Oliver, et al.), the disclosure of which is totally incorporated herein by reference, discloses a hot melt ink composition comprising (a) an ink vehicle, said ink vehicle being a solid at about 25° C. and having a viscosity of from about 1 to about 20 centipoise at a temperature suitable for hot melt ink jet printing, said temperature being greater than about 45° C., (b) a photochromic material, (c) an optional colorant, and (d) an optional propellant.
U.S. Pat. No. 5,551,973 (Oliver, et al.), the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises an aqueous phase, an oil phase, a photochromic material, and a surfactant, said ink exhibiting a liquid crystalline gel phase at a first temperature and a liquid microemulsion phase at a second temperature higher than the first temperature.
U.S. Pat. No. 5,759,729 (Martin, et al.), the disclosure of which is totally incorporated herein by reference, discloses a toner composition for the development of electrostatic latent images which comprises particles comprising a mixture of a resin and a photochromic material. U.S. Pat. No. 5,759,729 also discloses a liquid developer composition for the development of electrostatic latent images which comprises a nonaqueous liquid vehicle and a photochromic material, wherein the liquid developer has a resistivity of from about 108 to about 1011 ohm-cm and a viscosity of from about 25 to about 500 centipoise. U.S. Pat. No. 5,759,729 further discloses a liquid developer composition for the development of electrostatic latent images which comprises a nonaqueous liquid vehicle, a charge control agent, and toner particles comprising a mixture of a resin and a photochromic material.
U.S. Pat. No. 5,710,420 (Martin, et al.), the disclosure of which is totally incorporated herein by reference, discloses a method of embedding and recovering machine readable information on a substrate which comprises (a) writing data in a predetermined machine readable code format on the substrate with a photochromic marking material having a first state corresponding to a second absorption spectrum; and (b) thereafter effecting a photochromic change in at least some of the photochromic marking material from the first state to the second state.
James T. C. Wojtyk, Peter M. Kazmaier, and Erwin Buncel, “Effects of Metal Ion Complexation on the Spiropyran-Merocyanine Interconversion: Development of a Thermally Stable Photo-Switch,” Chem. Commun. 1998, p. 1703, the disclosure of which is totally incorporated herein by reference, discloses spectrophotometric absorption and fluorescence measurements of spiropyrans
modified with chelating functionalities, in the presence of Ca2+ and Zn2+, that provide evidence of a thermally stable spiropyran-merocyanine photoswitch that is modulated by the metal cations.
U.S. Pat. No. 6,358,655 B1, entitled “Marking Particles,” with the named inventors Daniel A. Foucher, Raj D. Patel, Naveen Chopra, and Peter M. Kazmaier, the disclosure of which is totally incorporated herein by reference, discloses marking particles comprising a resin, a chelating agent, and a spiropyran material which is of the formula
wherein n is an integer representing the number of repeat —CH2— units and R is —H or —CH═CH2. The marking particles are prepared by an emulsion aggregation process.
U.S. Pat. No. 6,365,312 B1 entitled “Marking Particles,” with the named inventors Daniel A. Foucher, Raj D. Patel, Naveen Chopra, Peter M. Kazmaier, Erwin Buncel, and James Wojtyk, the disclosure of which is totally incorporated herein by reference, discloses marking particles comprising a first polymer, a second polymer, a chelating agent, and a spiropyran material of the formula
wherein n is an integer representing the number of repeat —CH2— units and R is —H or —CH═CH2. The marking particles comprise a core containing the first polymer in which is dispersed the chelating agent and the spiropyran and encapsulated within a shell of the second polymer formulated by an interfacial polymerization.
U.S. Pat. No. 6,458,165 B1 entitled “Marking Particles,” with the named inventors Daniel A. Foucher, Raj D. Patel, Naveen Chopra, Peter M. Kazmaier, Erwin Buncel, and James Wojtyk, the disclosure of which is totally incorporated herein by reference, discloses an addressable display comprising a substrate having uniformly situated thereon a coating of marking particles comprising a first polymer, a second polymer, a chelating agent, and a spiropyran material of the formula
wherein n is an integer representing the number of repeat —CH2— units and R is —H or —CH═CH2. The marking particles comprise a core containing the first polymer in which is dispersed the chelating agent and the spiropyran and encapsulated within a shell of the second polymer formulated by an interfacial polymerization.
U.S. Pat. No. 6,652,959 B2, entitled “Marking Particles,” with the named inventors Daniel A. Foucher, Raj D. Patel, Naveen Chopra, and Peter M. Kazmaier, the disclosure of which is totally incorporated herein by reference, discloses an addressable display comprising a substrate having uniformly situated thereon a coating of marking particles comprising a resin, a chelating agent, and a spiropyran material which is of the formula
wherein n is an integer representing the number of repeat —CH2— units and R is —H or —CH═CH2. The marking particles are prepared by an emulsion aggregation process.
U.S. Pat. No. 6,517,618 B2 entitled “Photochromic Electrophoretic Ink Display,” with the named inventors Daniel A. Foucher, Raj D. Patel, Naveen Chopra, Peter M. Kazmaier, Erwin Buncel, and James Wojtyk, the disclosure of which is totally incorporated herein by reference, discloses an electrophoretic ink comprising a suspending fluid and, suspended in the suspending fluid, a plurality of particles comprising a mixture of a chelating agent and a spiropyran material of the formula
wherein n is an integer representing the number of repeat —CH2— units and R is —H or —CH═CH2, said particles being free to migrate within said suspending fluid under the influence of an electric field.
U.S. Pat. No. 6,549,327 B2 entitled “Photochromic Gyricon Display,” with the named inventors Daniel A. Foucher, Raj D. Patel, Naveen Chopra, Peter M. Kazmaier, Erwin Buncel, and James Wojtyk, the disclosure of which is totally incorporated herein by reference, discloses a display comprising an arrangement of a plurality of optically anisotropic rotatable elements, each of said rotatable elements having a surface in contact with an enabling fluid, said rotatable elements being electrically dipolar in the presence of the enabling fluid and thus being subject to rotation upon application of an electric field, said rotatable elements being free to rotate in place but not free to translate substantially so as to disrupt the arrangement of rotatable elements, wherein a first portion of said surface contains a mixture of a chelating agent and a spiropyran material of the formula
wherein n is an integer representing the number of repeat —CH2— units and R is —H or —CH═CH2, and wherein a second portion of said surface contains substantially no spiropyran.
In “Combinatorial Color Generation with Mixtures of Dithienyl Photochromes,” Adv. Mater. 1999, vol 11, p. 910-913, the disclosure of which is totally incorporated herein by reference, Alvaro Fernandez-Acebes and Jean-Marie Lehn discloses the generation of multi-colored images created by UV irradiation of dithienylethenes of the structure

While known compositions and processes are suitable for their intended purposes, a need remains for improved display characteristics. In addition, a need remains for displays comprised of marking particles with multicolored photochromic characteristics. Further, a need remains for processes for preparing documents with images having multicolored photochromic characteristics. Additionally, a need remains for processes and materials that enable the placement of encoded information on documents which is not detectable to the reader but which is machine readable. There is also a need for displays comprised of multicolored photochromic marking particles that are thermally stable. In addition, there is a need for displays using multicolored photochromic marking particles wherein both resonance forms of the photochromic material are stable. Further, there is a need for displays made of multicolored photochromic marking particles wherein the two resonance forms of the photochromic material are addressable at different wavelengths. Additionally, there is a need for displays made of multicolored photochromic marking particles wherein both resonance forms of the photochromic material are stable for reasonable periods of time without the need for constant irradiation to maintain the resonance form. A need also remains for materials and processes that generate images that cannot be easily or accurately photocopied or scanned.